Preparation of a dimethyltetralin

ABSTRACT

A method for preparing one or more specific dimethyltetralins from either 5-(o-, m-, or p-tolyl)-pent-1-or -2-ene or 5-phenyl-hex-1- or -2-ene, and optionally for preparing one or more specific dimethylnaphthalenes from the aforesaid dimethyltetralins is disclosed.

RELATED APPLICATION

This application is a continuation in part of pending patent application Ser. No. 316,308, filed on Feb. 27, 1989, which is a continuation in part of patent application Ser. No. 211,000, filed on Jun. 24, 1988, and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a method for preparing a dimethyltetralin and more particularly concerns a method for preparing primarily a specific dimethyltetralin or a mixture of specific dimethyltetralins from either 5-(o-, m-, or p-tolyl)- pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene in the presence of a Y-type crystalline aluminosilicate molecular sieve zeolite.

2. Description of the Prior Art

Naphthalene dicarboxylic acids are monomers that are known to be useful for the preparation of a variety of polymers. For example, poly(ethylene 2,6-naphthalate) prepared from 2,6-naphthalene dicarboxylic acid and ethylene glycol has better heat resistance and mechanical properties than polyethylene terephthalate and is useful in the manufacture of films and fibers.

Dimethylnaphthalenes are desirable feedstocks for oxidation to the corresponding naphthalene dicarboxylic acids. A known conventional process for producing a naphthalene dicarboxylic acid comprises the oxidation of a dimethylnaphthalene with oxygen in the liquid phase in an acetic acid solvent at an elevated temperature and pressure and in the presence of a catalyst comprising cobalt, manganese and bromine components.

Typically dimethylnaphthalenes are found in refinery or coal-derived streams as mixtures of all of the ten possible dimethylnaphthalene isomers. However, separation of these isomers is very difficult and expensive. Consequently, methods for producing specific dimethylnaphthalenes or mixtures of two or three specific dimethylnaphthalenes in high purity and quality are highly desirable. One type of such method is a multistep synthesis involving (1) the formation of an alkenylbenzene by the reaction of o-, m- or p-xylene or ethylbenzene with butadiene, (2) the cyclization of the resulting alkenylbenzene to form one or more dimethyltetralins belonging to one or two of three groups of three isomeric dimethyltetralins--that is, either group A containing the 1,5-, 1,6-, 2,5- and 2,6-dimethyltetralins, group B containing the 1,7-, 1,8-, 2,7- and 2,8-dimethyltetralins, or group C containing the 1,3-, 1,4-, 2,3-, 5,7-, 5,8- and 6,7-dimethyltetralins--(3) the dehydrogenation of the dimethyltetralin(s) to form the corresponding dimethylnaphthalene(s), and (4) the isomerization of the resulting dimethylnaphthalene(s) to the desired specific dimethylnaphthalene.

For example, Thompson, U.S. Pat. Nos. 3,775,496; 3,775,497; 3,775,498; 3,775,500 disclose processes for the cyclization of specific alkenylbenzenes to one or more specific dimethyltetralins at 200°-450° C. in the presence of any suitable solid acidic cyclization catalyst such as acidic crystalline zeolites as well as silica-alumina, silica-magnesia and silica-alumina-zirconia and phosphoric acid, followed by the dehydrogenation of the resulting dimethyltetralin(s) in the vapor state to the corresponding dimethylnaphthalene(s) in a hydrogen atmosphere at 300°-500° C. and in the presence of a solid dehydrogenation catalyst such as noble metals on carriers and chromia-alumina, and thereafter isomerization of each of the aforesaid dimethylnaphthalene(s) to the desired isomer within the triad of dimethylnaphthalenes to which the isomer being isomerized belongs, at 275°-500° C. in the presence of a solid acidic isomerization catalyst of the same type as described in respect of the cyclization disclosed therein. In the alternative, both the cyclization and isomerization reactions can be performed in the liquid phase, in which case the cyclization is performed at 200°-275° C. with a solid phosphoric acid catalyst, at 70°-140° C. with an acidic ion exchange resin, an acidic crystalline zeolite, hydrofluoric or sulfuric acid as the catalyst or a siliceous cracking catalyst.

More specifically, Thompson, U.S. Pat. No. 3,775,496 discloses the cyclization of 5-(m-tolyl) -pent-2-ene to 1,6- and 1,8-dimethyltetralins, which are then dehydrogenated to 1,6- and 1,8-dimethylnaphthalenes, which in turn are isomerized to 2,6- and 2,7-dimethyl-naphthalenes, respectively. Thompson, U.S. Pat. No. 3,775,497 discloses the cyclization of 5-phenyl-hex-2-ene to 1,4-dimethyltetralin which is then dehydrogenated to 1,4-dimethylnaphthalene, which is in turn isomerized to 2,3-dimethylnaphthalene. Thompson, U.S. Pat. No. 3,775,498 discloses the cyclization of 5-(o-tolyl)-pent-2-ene to 1,5-dimethyltetralin, which is then dehydrogenated to 1,5-dimethylnaphthalene, which is in turn isomerized to 2,6-dimethylnaphthalene. Thompson, U.S. Pat. No. 3,775,500 discloses the cyclization of 5-(p-tolyl)-pent-2-ene to 1,7-dimethyltetralin, which is then dehydrogenated to 1,7-dimethylnaphthalene, which in turn is isomerized to 2,7-dimethylnaphthalene.

Shimada et al., U.S. Pat. No. 3,780,119 disclose a method for the isomerization of dimethylnaphthalene by the use at a temperature above 260° C. of a mordenite catalyst in which a metal form of mordenite is in excess of 20 weight percent of the mordenite, with the metal being selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc and aluminum.

Suld et al., U.S. Pat. No. 3,803,253 disclose a method for the hydroisomerization of a dimethylnaphthalene by the use of a combination of a hydrogenation catalyst and a calcium-containing zeolite catalyst, such as a calcium-exchanged synthetic faujasite, for example, a Y-type molecular sieve.

Shima et al., U.S. Pat. No. 3,806,552 disclose a method for the isomerization of dimethylnaphthalenes in the gas phase by the use of a mixed catalyst consisting of (a) 65-95 weight percent of a hydrogen form of mordenite in which above 80 weight percent of the metal cations are replaced with hydrogen ions, and (b) 5-35 weight percent of catalyst selected from the group consisting of bentonite and fuller's earth.

Hedge, U.S. Pat. No. 3,855,328 discloses a method for the isomerization of dimethylnaphthalenes by the use of a Type Y alumino silicate zeolite at 120°-300° C. in the liquid phase. The catalysts have aluminum-to-silicon atomic ratios of 0.1-1.0.

Ogasawara et al., U.S. Pat. No.3,888,938 disclose a method for the isomerization of dimethylnaphthalenes in the liquid phase by the use of a mixed catalyst consisting of (a) 70-95 weight percent of a hydrogen form of mordenite in which above 80 weight percent of the metal cations are replaced with hydrogen ions, and (b) 5-30 weight percent of a promoter selected from the group consisting of bentonite and fuller's earth.

Hedge et al., U.S. Pat. No. 3,928,482 disclose the isomerization of either dimethyldecalins, dimethyltetralins or dimethylnaphthalenes in the presence of an alumino silicate zeolite containing polyvalent metal cations in exchange positions, such as a rare earth-exchanged Type Y zeolite.

Yokayama et al., U.S. Pat. No. 3,957,896 disclose the selective isomerization of dimethylnaphthalenes in the presence of any kind of natural or synthetic, solid acid catalyst, such as Y-type zeolite as well as silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-zirconia, fuller's earth, natural or synthetic mordenite, X-type zeolite, A-type zeolite and L-type zeolite. These catalysts may be substituted partly or wholly by hydrogen or metal. Furthermore, these catalysts can be unsupported or supported on carriers.

Onodera et al., U.S. Pat. No. 4,524,055 disclose a crystalline aluminosilicate zeolite that is useful in the isomerization of dimethylnaphthalenes and has a silica-to-alumina mole ratio of 10 to 100, specific x-ray lattice distances, and a specific cyclohexane-to-n-hexane adsorption ratio of at least 0.7.

Mak1 et a1., U.S. Pat. No. 4,556,751 disclose the isomerization of dimethylnaphthalenes in the presence of a crystalline aluminosilicate having a pentasil structure and a silica-to-alumina molar structure of 12 or higher. In addition, the aluminosilicate may contain some other metals as non-exchangeable metals.

A problem in all such prior art methods is the presence of other dimethylnaphthalene isomers and unconverted dimethyltetralin and alkenylbenzene as impurities and by-products in the finally obtained, desired specific dimethylnaphthalene isomer. The presence of such impurities and by-products markedly reduces the utility and commercial value of the desired dimethylnaphthalene isomer, especially as a precursor for the formation of a naphthalene dicarboxylic acid for use as a monomer in the manufacture of a polymer. In addition, catalysts tend to deactivate relatively rapidly at the high temperatures employed in vapor phase processes. Therefore, it is highly desirable to employ liquid phase processes and to improve the completeness of each step in the aforesaid multistep synthesis and the selectivity of each step therein for the production of the desired product therefrom.

In this regard, it is known that in the presence of an acid catalyst, the dimethylnaphthalene isomers are isomerizable within each triad of dimethylnaphthalene isomers--that is, within the 1,5-, 1,6- and 2,6-dimethylnaphthalenes of triad A, within the 1,7-, 1,8-, and 2,7-dimethylnaphthalenes of triad B, and within the 1,3-, 1,4- and 2,3-dimethylnaphthalenes of triad C. It is also known that the interconversion of a dimethylnaphthalene isomer within one of the aforesaid triads to a dimethylnaphthalene isomer within another of the aforesaid triads occurs to a relatively lesser extent. Consequently, it is highly desired to improve the selectivity of the cyclization step in the aforesaid multistep synthesis for the formation of dimethyltetralin isomers that belong to the same triad to which also belongs the specific desired dimethyltetralin isomer, which upon dehydrogenation is converted to the desired specific corresponding dimethylnaphthalene isomer. It is also highly desired to improve the selectivity and completeness of the isomerization step in the aforesaid multistep synthesis for the formation of the specific dimethylnaphthalene isomer desired.

OBJECTS OF THE INVENTION

It is therefore a general object of the present invention to provide an improved method for manufacturing with an improved yield and selectivity a specific dimethyltetralin isomer or set of dimethyltetralin isomers by the cyclization of an alkenylbenzene which meets the aforementioned requirements for selectivity and completeness and catalyst activity.

It is a related object of the present invention to provide an improved method for manufacturing with an improved yield and selectivity a specific dimethylnaphthalene isomer or set of dimethylnaphthalene isomers by the cyclization of an alkenylbenzene to form a specific dimethyltetralin isomer or set of dimethyltetralin isomers and then dehydrogenating the dimethyltetralin(s).

It is another related object of the present invention to provide an improved method for manufacturing with an improved yield and selectivity a specific dimethylnaphthalene isomer or set of specific dimethylnaphthalene isomers by the cyclization of an alkenylbenzene to form a specific dimethyltetralin isomer or set of dimethyltetralin isomers and then dehydrogenating the dimethyltetralin(s) and isomerizing the resulting dimethylnaphthalene(s).

Other objects and advantages of the method of the present invention will become apparent upon reading the following detailed description and appended claims.

SUMMARY OF THE INVENTION

The objects are achieved by an improved method for preparing a dimethyltetralin from 5-(o-, m-, or p-to-lyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene as the first feedstock, comprising: contacting the first feedstock in liquid form with a solid cyclization catalyst comprising a Y-type, crystalline aluminosilicate molecular sieve zeolite that is substantially free of adsorbed water, and at an elevated temperature and at a pressure that is sufficiently high to maintain the first feedstock substantially in the liquid phase, to thereby cyclize the first feedstock to form a first liquid product comprising a mixture of dimethyltetralins, wherein, if present, the concentration of water in the first feedstock is less than about 0.5 weight percent, based on the weight of the feedstock, wherein either (a) the first feedstock comprises 5-(o-tolyl)-pent-1- or -2-ene and 1,5-, 1,6-, 2,5- or 2,6-dimethyltetralin or mixtures thereof comprise at least 80 weight percent of the mixture of dimethyltetralins formed, (b) the first feedstock comprises 5-(m-tolyl)-pent-1- or -2-ene and 1,5-, 1,6-, 1,7-, 1,8-, 2,5-, 2,6-, 2,7-, or 2,8-dimethyltetralin, or mixtures thereof comprise at least 80 weight percent of the mixture of dimethyltetralins formed, (c) the first feedstock comprises 5-(p-tolyl)-pent-1- or -2-ene and 1,7-, 1,8-, 2,7-, or 2,8-dimethyltetralin, or mixtures thereof comprise at least 80 weight percent of the mixture of dimethyltetralins formed, (d) the first feedstock comprises 5-phenyl-1-or -2-hexene and 1,3-, 1,4-, 2,3-, 5,7-, 5,8- or 6,7-dimethyltetralin or mixtures thereof comprise at least 80 weight percent of the mixture of dimethyltetralins formed.

This invention is also a method for preparing one or more dimethyltetralins from 5-(o-,m-, or p-tolyl)-pent-1-or -2-ene or 5-phenyl-hex-1- or -2-ene as the first feedstock, comprising: contacting the first feedstock in liquid form with a solid cyclization catalyst comprising an acidic ultra-stable crystalline aluminosilicate molecular sieve Y-zeolite that has a silica-to-alumina molar ratio of from about 4:1 to about 10:1, pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from about 24.2 to about 24.7 angstroms, and that contains from about 0.05 up to about 3.5 weight percent of sodium, calculated as elemental sodium, and based on the weight of the zeolite and that is substantially free of adsorbed water, and at an elevated temperature and at a pressure that is sufficiently high to maintain the first feedstock substantially in the liquid phase, to thereby cyclize the first feedstock to form a first liquid product comprising one or more dimethyltetralins, wherein water is at a concentration in the first feedstock of from zero up to less than about 0.5 weight percent, based on the weight of the feedstock, wherein (1) when the first feedstock comprises 5-(o-tolyl)-pent-1-or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,5-, 1,6-, 2,5- or 2,6-dimethyltetralin or a mixture thereof, (2) when the first feedstock comprises 5-(m-tolyl)-pent-1- or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,5-, 1,6-, 1,7-, 1,8-, 2,5-, 2,6-, 2,7- or 2,8-dimethyltetralin or a mixture thereof, (3) when the first feedstock comprises 5-(p-tolyl)-pent-1-or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof, or (4) when the first feedstock comprises 5-phenyl-hex-1- or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised of 1,3-, 1,4-, 2,3-, 5,7-, 5,8- or 6,7-dimethyltetralin or a mixture thereof.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail by the results presented in the accompanying drawing and described below by way of examples of the invention. In the drawing, FIG. 1 is a series of plots of the yields of 1,5-dimethyltetralin from the cyclization of 5-o-tolyl-2-pentene in Examples 19-23 involving 5 different cyclization catalysts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Suitable feedstocks for use in the cyclization of the method of the present invention are 5-(o-, m-, or p-to-lyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene. In the method of the present invention, the cyclization step is followed preferably by a dehydrogenation step and more preferably by first a dehydrogenation step and second an isomerization step.

When 5-(o-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step of the present invention, 1,5-, 1,6-, 2,5-, or 2,6-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which resulting dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step of the present invention to the corresponding 1,5-, 1,6- and 2,6-dimethylnaphthalenes, which are then the feedstock in the isomerization step of the present invention and are converted therein to 2,6-dimethylnaphthalene.

When 5-(m-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step, 1,5- 1,6- 1,7-, 1,8- 2,5- 2,6-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding 1,5-, 1,6-, 1,7-, 1,8- 2,6- and 2,7-dimethylnaphthalenes, which are then the feedstock in the isomerization step and are converted to 2,6- and 2,7-dimethylnaphthalenes.

When 5-(p-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step, 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding 1,7-, 1,8- and 2,7-dimethylnaphthalenes which are then the feedstock and are converted in the isomerization step to 2,7-dimethylnaphthalene.

When 5-phenyl-1- or -2-hexene is the feedstock to the cyclization step, 1,3-, 1,4-, 2,3-, 5,7, 5,8-, or 6,7-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding, 1,3-, 1,4- and 2,3-dimethylnaphthalenes, which are then the feedstock in the isomerization step and are converted to 2,3-dimethylnaphthalene.

In the method of the present invention, each of the aforesaid cyclization, dehydrogenation and isomerization reactions is performed in the liquid phase at an elevated temperature and at a sufficiently high pressure to ensure that the feedstock for the particular step is maintained in the liquid phase. By elevated temperature it is meant a temperature sufficiently high so that a significant portion of the feedstock for the respective reaction is converted to the desired product using preselected catalyst levels and reaction times for batch processes, or preselected space velocities for continuous processes. Preferably, the cyclization reaction is performed at a temperature in the range of about 120° C., more preferably about 150° C., to about 400° C., more preferably to about 320° C. Most preferably the cyclization reaction is performed at a temperature in the range of about 150° C. to about 300° C. The cyclization reaction is preferably performed at a pressure in the range of about 0.05, more preferably about 0.1, to about 20.0, more preferably to about 5.0 atmosphere absolute. The dehydrogenation reaction is preferably performed at a temperature in the range of about 200° C., more preferably about 220° C., to about 500° C., more preferably to about 450° C. Most preferably, the dehydrogenation reaction is performed at a temperature in the range of about 220° C. to about 420° C. Preferably, the dehydrogenation reaction is performed at a pressure in the range of about 0.1, more preferably about 1.0, to about 30.0, more preferably to about 20.0 atmospheres absolute. The isomerization reaction is preferably performed at a temperature in the range of about 200° C., more preferably about 240° C., to about 420° C., more preferably to about 380° C. Most preferably the isomerization reaction is performed at a temperature in the range of about 240° C. to about 350° C. The isomerization reaction is preferably performed at a pressure in the range of about 0.1, more preferably about 0.5, to about 20.0, more preferably 5.0 atmospheres absolute.

Each of the cyclization, dehydrogenation and isomerization reactions can be performed with or without a solvent for the respective feedstock. Preferably a solvent is not employed in the aforesaid steps. If employed, a solvent in any of the aforesaid steps must be inert under the conditions employed and suitably comprise a paraffin such as a tetradecane, or an aromatic hydrocarbon such as anthracene, or mixtures thereof, which preferably boils above about 270° C. In the cyclization step, if water is present, its concentration is less than 0.5 weight percent, preferably less than 0.1 weight percent, based on the weight of the alkenylbenzene feedstock. More preferably, water is not present in the cyclization reaction medium.

Each of the cyclization, dehydrogenation and isomerization steps of the method of the present invention can be performed either batchwise or continuously. The reaction apparatus to be used in each aforesaid step can be of any known type such as a fixed bed, moving bed, fluidized bed, liquid phase suspended bed or a solid-liquid mixture in a stirred tank. Generally, however, the use of a fixed bed is commercially preferred for continuous operation. When conducting the dehydrogenation reaction of this invention in a continuous manner, it is advantageous to use two or more fixed bed reactors in series. Hydrogen formed during the dehydrogenation reaction is preferably removed from the product mixture between such fixed bed reactors arranged in series.

The improved conversion of the feedstock and selectivity for the production of the desired product or set of products for each of the cyclization, dehydrogenation and isomerization steps of the method of this invention are the result of the temperature and pressure conditions employed and the high activity and selectivity of the catalysts employed in each aforesaid step, which in turn permits the use of less severe conditions such that greater selectivity and reduced catalyst deactivation can be achieved.

The catalyst employed in the cyclization step of the method of this invention comprises an acidic ultrastable--that is, a thermally stabilized or dealuminated--Y-type crystalline aluminosilicate zeolite having a silica-to-alumina molar ratio of from about 4:1, preferably from about 5:1, to about 10:1, preferably to about 6:1, and having pore windows provided by twelve-membered rings containing oxygen, and a unit cell size of from about 24.2, preferably from about 24.3, to about 24.7, preferably to about 24.6 angstroms. A suitable such zeolite is marketed by Union Carbide under the name LZ-Y72 or LZ-Y20.

The zeolite is preferably substantially free of adsorbed water. If present on the zeolite, the adsorbed water can be removed from the zeolite by heating it in a dry atmosphere at about 250° C. for 0.5-1 hour. In the alternative, and less preferably, the presence of absorbed water at a concentration of up to 15 weight percent of the catalyst can be tolerated if a reaction temperature in the aforesaid range of at least 180° C. is employed.

The aforesaid zeolite employed in the catalyst for the cyclization step of the method of this invention is in the hydrogen form and contains from about 0.05, up to about 3.5 weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite. If the cyclization step is performed batchwise, the cyclization catalyst preferably contains from about 1 to about 3.5 weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite. If the cyclization step is performed continuously, the cyclization catalyst preferably contains from about 0.05 to about 0.5 weight percent, calculated as elemental sodium and based on the weight of the zeolite. Preferably, the cyclization catalyst contains from about 0.01, preferably from about 0.05, to about 3, preferably to about 1.5 weight percent of a component comprising a first metal selected from the group consisting of platinum, palladium, iridium and rhodium, calculated as the elemental metal and based on the weight of the catalyst. Most preferably this metal component comprises platinum.

More preferably, especially when the cyclization is performed continuously, the cyclization catalyst also contains from about 0.01, preferably from about 1, to about 5, preferably to about 3 weight percent of a component comprising a second metal selected from the group consisting of copper, tin, gold, lead and silver, calculated as the elemental metal and based on the weight of the catalyst. More preferably this second metal component comprises copper, tin or gold.

The aforesaid zeolite can be employed either unsupported or supported on a porous refractory, inorganic oxide that is inert under the conditions employed, such as silica, alumina, silica-alumina, magnesia, bentonite or other such clays. If a support is employed, preferably the support comprises silica, alumina, or silica-alumina. When a support is employed, the zeolite comprises from about 10, preferably from about 20, to about 90, preferably to about 80 weight percent based on the weight of the catalyst.

If the cyclization is performed on a batch basis, the catalyst is employed at a level in the range of from about 0.1, preferably from about 1.0, to about 5, preferably to about 3 weight percent of the zeolite component of the catalyst, based on the weight of the alkenylbenzene feedstock, and the reaction time is from about 0.5, preferably from about 2, to about 10, preferably to about 6 hours. If the cyclization is performed on a continuous basis, the space velocity is in the range of from about 0.1, preferably from about 1, to about 20, preferably to about 10, parts of alkenylbenzene feedstock per part of zeolite component of the catalyst by weight per hour.

The catalyst employed in the dehydrogenation step of the method of this invention is any solid dehydrogenation catalyst that is capable of affecting the dehydrogenation and exhibiting a reasonable lifetime under the conditions employed, including catalysts such as noble metals on carriers such as reforming catalysts. Aluminas, silicas, alumina-silicas, and activated carbons are examples of suitable carriers or supports. The noble metals include, for example, platinum, palladium, ruthenium and rhenium. The noble metal component can also comprise mixtures of two or more noble metals. Preferably, palladium on an active carbon or alumina support containing from about 0.5, more preferably from about 1.0, to about 15, more preferably to about 10 weight percent of palladium, calculated as elemental palladium and based on the weight of the catalyst, is employed as the dehydrogenation catalyst.

Other preferred dehydrogenation catalysts include platinum on activated carbon or alumina supports, rhenium on activated carbon or alumina supports and mixtures of platinum and rhenium on activated carbon or alumina supports, wherein the platinum and rhenium are each present from about 0.01, preferably 0.05, to about 10.0, preferably 5.0 weight percent calculated as the element and based on the weight of the catalyst. A more preferred dehydrogenation catalyst comprises a mixture of platinum and rhenium on gamma alumina where the platinum and rhenium are each present in the range of about 0.1 to about 1.0 weight percent calculated as the element, and based on the weight of the catalyst. A support material such as an alumina or other non-combustible support material has an advantage over a carbon support material in that the non-combustible support can be exposed to air or other source of oxygen-containing gas at an elevated temperature to regenerate a deactivated catalyst. Consequently, such a catalyst can be cycled wherein between each cycle of use as a dehydrogenation catalyst the catalyst is regenerated with an oxygen-containing gas at an elevated temperature. Preferably the level of oxygen in the oxygen-containing gas is about 1 wt% to about 25 wt%, the regeneration temperature is in the range of about 400° C. to about 600° C. and the time of exposure to the oxygen-containing gas at these temperatures is that sufficient to regenerate the catalyst.

In the liquid phase dehydrogenation reactions of this invention, when conducted in either a batch or continuous manner, and particularly when using the preferred dehydrogenation catalysts, the addition of hydrogen to the reaction mixture is not necessary to maintain catalyst activity during extended catalyst use, i.e., the liquid phase dehydrogenation reaction in the method of this invention wherein a dimethyltetralin is dehydrogenated to a dimethylnaphthalene proceeds in the absence of hydrogen added to the reaction mixture. Without intending to be bound by a theory of operation, it appears that during the liquid phase dehydrogenation method of this invention wherein dimethyltetralins are dehydrogenated to dimethylnaphthalenes using a dehydrogenation catalyst, and particularly the preferred noble metal dehydrogenation catalysts disclosed herein, the hydrogen generated during the dehydrogenation reaction effectively maintains catalyst activity.

In the dehydrogenation method of this invention it is advantageous to remove hydrogen during the liquid phase dehydrogenation reaction. This is accomplished in a batch procedure by venting the hydrogen from the vessel used to conduct the batch reaction. If operating in a continuous mode, a plurality of series arranged fixed bed reactors can be utilized with the hydrogen vented from the process stream between fixed bed reactors.

If the dehydrogenation is performed on a batch basis, the catalyst is employed at a level in the range of from about 0.005, preferably from about 0.01, to about 1.0, preferably to about 0.2 weight percent of the noble metal component, calculated as the elemental noble metal and based on the weight of the dimethyltetralin feedstock, and the reaction time is from about 1, preferably from about 2, to about 50, preferably to about 40 hours. If the dehydrogenation is performed on a continuous basis, the space velocity is in the range of from about 0.1, preferably from about 10, to about 5000, preferably to about 2000 parts of the dimethyltetralin feedstock per part of the noble metal component (calculated as the elemental noble metal) of the catalyst by weight per hour.

The catalyst employed in the isomerization step of the method of this invention comprises either beta zeolite or an acidic ultrastable--that is, a thermally stabilized or dealuminated--Y-type crystalline aluminosilicate zeolite having a silica-to-alumina molar ratio of from about 4:1 preferably from about 5:1, to about 10:1, preferably to about 6:1, and having pore windows provided by twelve-membered rings containing oxygen, and a unit cell size of from about 24.2, preferably from about 24.3, to about 24.7, preferably to about 24.6 angstroms. A suitable such zeolite is marketed by Union Carbide under the name LZ-Y72 or LZ-Y20. Water is not detrimental to catalytic activity or selectivity in the isomerization process.

The isomerization catalyst preferably comprises beta zeolite. The composition, structure and preparation of beta zeolite are described in Wadlinger et al., U.S. Pat. No. 3,308,069 which in its entirety is specifically incorporated herein by reference. The structure of beta zeolite is also reported in J. Haggin, "Structure of Zeolite Beta Determined," in Chemical & Engineering News, p. 23 (Jun. 20, 1988). Beta zeolite is also commercially available from PQ Corporation.

The aforesaid ultrastable Y-type zeolite which can be employed in the catalyst for the isomerization step of the method of this invention is in the hydrogen form and contains from about 0.01, preferably from about 1, up to about 5, preferably up to about 3, weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite.

Preferably the isomerization catalyst comprises a hydrogenation component comprising a Group VIII metal, which more preferably is palladium, platinum or nickel.

The aforesaid zeolite of the isomerization catalyst can be employed either unsupported or supported on a porous refractory, inorganic oxide that is inert under the conditions employed, such as silica, alumina, silica-alumina, magnesia, bentonite or other such clays. If a support is employed, preferably the support comprises silica, alumina or silica-alumina. When a support is employed, the zeolite comprises from about 10, preferably from about 20, to about 90, preferably to about 80 weight percent based on the weight of the catalyst.

If the isomerization is performed on a batch basis, the catalyst is employed at a level in the range of from about 0.1, preferably from about 1.0, to about 5, preferably to about 3 weight percent of the zeolite component of the catalyst, based on the weight of the dimethylnaphthalene feedstock, and the reaction time is from about 0.5, preferably from about 2, to about 10, preferably to about 6 hours. If the isomerization is performed on a continuous basis, the space velocity is in the range of from about 0.1, preferably from about 0.5 to about 20, preferably to about 10 parts of dimethylnaphthalene feedstock per part of zeolite component of the catalyst by weight per hour.

For each of the cyclization, dehydrogenation, and isomerization reactions described hereinabove, it is preferable to conduct each reaction at the lowest possible reaction temperature that provides for the conversion of a significant portion of the reaction feedstock to the respective product. At elevated reaction temperatures, coke, tars and other reaction sideproducts tend to form more rapidly and deposit on and deactivate the catalysts disclosed herein. However, regardless of the reaction temperature used, as the catalyst ages catalytic activity typically decreases. This decrease in catalyst activity, which results in reduced feedstock conversion at preselected reaction conditions such as reaction pressure, catalyst level, space velocity and reaction temperature, can be offset somewhat by increasing the reaction temperature. Consequently, a preferred procedure for maximizing the useful life of the cyclization, dehydrogenation and isomerization catalysts of this invention is to begin using the catalysts at as low a reaction temperature that provides for the conversion of a significant portion of the respective feedstock and then increase the temperature of the reaction as the catalyst ages so as to maintain desirable feedstock conversion levels. For example, when using a batch process, the temperature of the reaction can be raised with each successive batch. When using a continuous process, the reaction temperature of the catalyst bed or continuous stirred tank reactor can be raised as the catalyst ages. When using an aged, i.e., partially deactivated, cyclization catalyst in the method of this invention, a reaction temperature greater than 250 ° C. is suitable for maintaining the conversion of a significant portion and preferably at least about 50 wt% and more preferably at least about 70 wt% of the cyclization reaction feedstock to the desired product or products. Preferably this temperature is in the range of from about 255° C. to about 400° C. and more preferably in the range of from about 260° C. to about 320° C. When employing an aged dehydrogenation catalyst in the method of this invention, a reaction temperature greater than 300° C. is suitable for maintaining the conversion of a significant portion and preferably at least about 50 wt% and more preferably at least about 70 wt% of the dehydrogenation reaction feedstock to the desired product or products. Preferably this temperature is in the range of from about 305° C. to about 500° C., and more preferably in the range of from about 310° C. to about 450° C. When using an aged isomerization catalyst in the method of this invention, a reaction temperature greater than 300° C. is suitable for maintaining the conversion of a significant portion and preferably at least about 20 wt% of the isomerization reaction feedstock to the desired product or products. Preferably this temperature is in the range of from about 305° C. to about 420° C., more preferably in the range of from about 310° C. to about 380° C.

Patent application USSN 316,308 filed on Feb. 27, 1989 is hereby specifically incorporated by reference.

The present invention will be more clearly understood from the following specific examples.

EXAMPLES 1-8

In each of Examples 1-8, 20-1000 grams of an alkenylbenzene were introduced into a stirred glass reactor, and dry nitrogen gas was employed to continuously purge the reaction medium to preclude moisture therefrom. The alkenylbenzene employed was 5-(o-tolyl)-pentene-2 in Examples 1-6, 5-(p-tolyl)-pentene-2 in Example 7 and 4-phenyl-pentene-2 in Example 8. Unsupported ultrastable Y-type crystalline aluminosilicate molecular sieve catalyst (Union Carbide's LZ-Y72) having a unit cell size of 24.51Å and containing 2.5 weight percent of sodium (calculated as sodium oxide) was added slowly to the alkenylbenzene in the reactor at a temperature below commencement of the cyclization of the alkenylbenzene. The catalyst was in the form of an unsupported powder in Examples 1-4, 7 and 8, and in the form of pellets containing 80 weight percent of the same sieve supported on 20 weight percent of an alumina support in Examples 5 and 6. The catalyst was maintained under dry, moisture-free conditions prior to use in Examples 1-3 and 5-8 but was allowed to adsorb moisture from air saturated with moisture at 30°-60° C. in Example 4. The catalyst employed in Example 4 contained 10-20 weight percent of water.

The temperature of the reaction medium was then raised quickly to the desired reaction temperature. Samples of the resulting reaction product were withdrawn from the reactor at various reaction times and analyzed to monitor the reaction. The desired cyclized product was 1,5-dimethyltetralin in Examples 1-6, 1,7-dimethyltetralin in Example 7 and 1,4-dimethyltetralin in Example 8. The experimental conditions employed, the compositions of the feedstock employed and of the resulting products containing up to 13 carbon atoms and the percent conversion of the alkenylbenzene feedstock, and the percent selectivity of the formation of desired product from the total amount of alkenylbenzene converted for each of Examples 1-8 are presented in Table 1. For the calculation of this percent selectivity, the desired product is the sum of 1,5-dimethyltetralin and 1,5-dimethylnaphthalene in Examples 1-6, the sum of 1,7-dimethyltetralin and 1,7-dimethylnaphthalene in Example 7, and the sum of 1,4-dimethyltetralin and 1,4-dimethylnaphthalene in Example 8.

Comparison of the results of Examples 2 and 4 illustrates that, even at the low feed-to-catalyst weight ratio employed in Example 4, the presence of a large concentration of water therein resulted in substantially reduced percents conversion, even after a reaction time of about 12 hours.

                                      TABLE 1                                      __________________________________________________________________________                Example 1   Example 2   Example 3                                                                               Example 4                                     Feed-       Feed-       Feed-    Feed-                                         stock                                                                              Product stock                                                                              Product stock                                                                              Product                                                                             stock                                                                              Product                        __________________________________________________________________________     Reaction Conditions                                                            Reaction time (hrs)                                                                       0   4   6   0   3   6.8 0   0.5  0   6.8  12.8                      Temperature (°C.)                                                                      148 148     168 168     243      170  170                       Pressure (psig)                                                                               1.0 1.0     1.0 1.0     1.0      0.0  0.0                       Feed/Catalyst (wt.)                                                                           50.1                                                                               50.1    50.1                                                                               50.1    49.9     43.5 43.5                      Composition (wt. %)                                                            Aryl-pentene feed                                                                         98.6                                                                               3.4 1.1 98.6                                                                               1.7 0   93.6                                                                               0    96.1                                                                               68.3 52.5                      Solvent    0.1 0.6 0.4 0.1 0   0   0   0.7  0.3 0.0  0.0                       Desired Products                                                               1,5-DMT        89.2                                                                               92.5    91.2                                                                               93.5                                                                               4.1 86.2 1.1 26.8 41.0                      1,5-DMN        0   0       0.5 1.2 0.1 2.3  0   0.1  0.3                       By-Products                                                                    Intermediate   3.2 2.5     2.5 0   0   0    0.3 2.0  2.9                       DMT isomers                                                                               0   0.4 0.4 0   0.6 0.6 0.1 1.4  0.0 0.4  0.6                       Aryl-pentane                                                                              0.2 0.3 0.5 0.2 0.9 2.0 0.3 4.4  0.4 0.2  0.1                       1,4-DMN        0   0       0   0   0   0        0.0  0.0                       1,7-DMN        0   0       0   0   0   0        0.0  0.0                       Lights     0.1 1.3 1.0 0.1 0.1 0   0.2 1.5  0.5 0.4  0.5                       Heavies    0   0   0   0   0.3 0.4 0   0.1  0.0 0.0  0.0                       Other      1.0 1.5 1.5 1.0 2.3 2.2 1.5 3.2  1.4 1.5  2.0                       Total      100.0                                                                              99.9                                                                               100.0                                                                              100.0                                                                              100.0                                                                              100.0                                                                              99.9                                                                               99.8 100.1                                                                              99.8 99.9                      % Conversion   96.6                                                                               98.9    98.3                                                                               100.0   100.0    28.9 45.4                      % Selectivity  93.7                                                                               94.9    94.6                                                                               96.0    90.2     92.8 94.6                      __________________________________________________________________________                  Example 5  Example 6  Example 7  Example 8                                     Feedstock                                                                            Product                                                                             Feedstock                                                                            Product                                                                             Feedstock                                                                            Product                                                                             Feedstock                                                                            Product                    __________________________________________________________________________     Reaction Conditions                                                            Reaction time (hrs)                                                                         0     4    0     11   0     8.5  0     3                          Temperature (°C.)                                                                          171        201        170        170                        Pressure (psig)    0.0        0.0        1.0        1.0                        Feed/Catalyst (wt.)                                                                               8.3        40.0       51.0       56.0                       Composition (wt. %)                                                            Aryl-pentene feed                                                                           97.6  0.0  97.6  5.2  99.0  3.3  98.3  0.5                        Solvent      0.9   0.1  0.9   0.0  0.0        0.8   0.0                        Desired Products                                                               1,5-DMT      0.0   84.1 0.0   75.6       90.0       92.7                       1,5-DMN            2.2        0.0        0.0        0.0                        By-Products                                                                    Intermediate 0.2   0.0  0.2   0.3                                              DMT isomers  0.1   1.2  0.1   1.3        1.3                                   Aryl-pentane 0.1   4.0  0.1   3.9        2.9        2.5                        1,4-DMN            0.0        0.0        0.0        1.6                        1,7-DMN            0.0        2.4        1.5        0.0                        Lights       0.0   0.1  0.0   0.1                                              Heavies      0.0   0.4  0.0   0.3                                              Other        0.0   7.5  0.9   10.8 1.1   1.0  1.0   2.8                        Total        99.7  99.7 99.7  99.9 100.0 100.0                                                                               100.0 100.0                      % Conversion       100.0      94.7       96.6       99.5                       % Selectivity      88.5       84.4       95.7       96.4                       __________________________________________________________________________

EXAMPLES 9-23

In each of Examples 9-23, a cyclization catalyst was packed into a stainless steel reactor, and the reactor was immersed into a fluidized sand bath at the desired reaction temperature. A mixture of 5-o-tolyl-2-pentene in the liquid phase and nitrogen was passed continuously through the reactor. At least once during at least one catalyst cycle, the resulting product stream was sampled and analyzed. The experimental conditions employed, the compositions of the feedstock employed and of the resulting products containing up to 13 carbon atoms, the percent conversion of the alkenylbenzene feedstock, and the percent selectivity of the formation of desired product from the total amount of alkenylbenzene converted in each of Examples 9-23 are presented in Table 2.

A catalyst cycle was concluded by discontinuing the flow of the 5-o-tolyl-2-pentene into the reactor and then purging the reactor at the reaction temperature with nitrogen to remove the hydrocarbons. The reactor was next heated to 500° C, and purged with air until the carbon dioxide content of the reactor effluent was less than 0.1 weight percent. This procedure resulted in the regeneration of the catalyst. The reactor was then cooled to the desired reaction temperature, and then the mixture of 5-o-tolyl-2-pentene in the liquid phase and nitrogen was passed continuously into the reactor.

In each of Examples 9-12 and 19-23, the reactor had an outside diameter of 0.25 inch, an inside diameter of 0.18 inch, a length of 5.5 inches, and one gram of the catalyst was packed into the reactor. In each of Examples 13-18, the reactor had an outside diameter of 0.375 inch, an inside diameter of 0.28 inch, a length of 5 inches, and 2.5 grams of the catalyst were packed into the reactor.

In each of Examples 9-14, an unsupported ultra-stable Y-sieve containing platinum and copper components was employed. This catalyst was prepared by adding to 30 grams of the commercial ultra-stable Y-sieve (Union Carbide's LZ-Y20) 15 milliliters of distilled water and 30 grams of an aqueous solution containing 1 weight percent of H₂ PtCl₆.6H₂ O, calculated as platinum, and 2 weight percent of copper in the form of cupric nitrate and calculated as elemental copper. The resulting slurry was mixed until it was uniform and then dried. The resulting solid was calcined at 500° C. in air for 4 hours, crushed and screened to obtain 0.0164-0.0278 inch (24-40 mesh) particles.

In each of Examples 15-18, a supported ultra-stable Y-sieve containing platinum and copper components was employed. This catalyst was prepared by crushing and screening a commercial sample of particles containing 80 weight percent of Union Carbide's LZ-Y20 supported on 20 weight percent of alumina to yield particles in the range of 24-40 mesh. To 10 grams of the supported sieve was added 11 milliliters of 0.9 weight percent of H₂ PtCl₆, calculated as platinum, and 1.8 weight percent of copper in the form of cupric nitrate, calculated as elemental copper. The resulting slurry was mixed until it was uniform and then dried. The resulting solid was calcined at 500° C. in air for 4 hours.

Each of Examples 19-23 were performed using the apparatus and procedure of Examples 9-12 at a reaction temperature of 154° C. and a space velocity of 1.1. The diluent gas was helium in Examples 19 and 20, hydrogen in Examples 21 and 22 and nitrogen in Example 23. The molar ratio of diluent-to-5-o-tolyl-2-pentene was 1.3 in Example 19 and 2.1 in each of Examples 20-23. The catalyst was unsupported in each example, and was ultra-stable Y-sieve (Union Carbide's LZ-Y20) in Example 19, ultra-stable Y-sieve containing 2 weight percent of copper in the form of cupric nitrate, (calculated as elemental copper) in each of Examples 20 and 21, ultra-stable Y-sieve treated with SiCl₄ in Example 22 and ultra-stable Y-sieve containing 2 weight percent of copper in the form of cupric nitrate (calculated as elemental copper) and 1 weight percent of platinum in the form of H₂ PtCl₆ (calculated as elemental platinum) in Example 23. In each of Examples 19-23, samples of the product stream were taken at several times after the beginning of the catalyst cycle and analyzed. From these measurements the yields of 1,5-dimethyltetralin were calculated and in FIG. 1 are plotted versus the number of hours since the respective catalyst had been regenerated.

The results indicate that the addition of copper to the sieve or the treatment of the sieve with silicon tetrachloride improves the selectivity of the catalyst but that the catalytic activity decreases with time. However, the addition of both platinum and copper to the sieve affords both substantially improved selectivity and excellent catalyst activity maintenance.

                                      TABLE 2                                      __________________________________________________________________________                                         Example                                                     Example            Exam-                                                                              Exam-  Example                                       Feed                                                                              9   10  11  12  Feed                                                                              ple 13                                                                             ple 14                                                                             Feed                                                                              15  16  17  18                  __________________________________________________________________________     Reaction Conditions                                                            Hours on stream  62.5                                                                               69.0                                                                               186.5                                                                              192.75 167 421.75 15.00                                                                              10.50                                                                              162.25                                                                             306.27              since regeneration                                                             Catalyst cycle no.                                                                              1   2   2   2      5   5      1   2   5   5                   Temperature (°C.)                                                                        154 153 153 204    153 153    152 154 153 163                 Pressure (psig)  73.5                                                                               19.5                                                                               32.5                                                                               53.5   3   11     2   2   2   2                   Space velocity (wt. feed/                                                                       1.07                                                                               1.08                                                                               2.20                                                                               2.20   1.14                                                                               1.25   1.20                                                                               1.22                                                                               1.20                                                                               1.23                wt. catalyst/hour)                                                             Composition (wt. %)                                                            Feed                                                                           Aryl-pentene  97.80                                                                             0.04                                                                               0.02                                                                               6.81                                                                               0.93                                                                               97.28                                                                             0.00                                                                               0.02                                                                               98.30                                                                             1.01                                                                               0.00                                                                               0.00                                                                               0.00                Diluent/Aryl-pentene                                                                            2.16                                                                               2.26                                                                               2.22                                                                               2.22   2.69                                                                               0.44   2.53                                                                               2.49                                                                               2.13                                                                               2.15                mole ratio                                                                     Desired Products                                                               1,5-DMT       0.0                                                                               83.99                                                                              94.36                                                                              87.02                                                                              84.53                                                                              0.00                                                                              94.45                                                                              94.48                                                                              0.00                                                                              81.97                                                                              93.14                                                                              95.18                                                                              94.79               1,5-DMN       0.0                                                                               2.54                                                                               0.95                                                                               0.10                                                                               4.18                                                                               0.00                                                                              0.26                                                                               0.35                                                                               0.00                                                                              1.59                                                                               1.88                                                                               0.70                                                                               0.68                By-Products                                                                    Intermediate  0.11                                                                              0.00                                                                               0.00                                                                               3.02                                                                               0.36                                                                               0.32                                                                              0.47                                                                               0.13                                                                               0.31                                                                              1.31                                                                               0.00                                                                               0.00                                                                               0.00                DMT isomers   0.11                                                                              0.39                                                                               0.03                                                                               0.55                                                                               0.86                                                                               0.25                                                                              0.03                                                                               0.30                                                                               0.17                                                                              1.53                                                                               0.39                                                                               0.32                                                                               0.42                DMN isomers   0.0                                                                               0.11                                                                               0.00                                                                               0.05                                                                               0.41                                                                               0.00                                                                              0.00                                                                               0.02                                                                               0.00                                                                              0.00                                                                               0.00                                                                               0.00                                                                               0.00                Aryl-pentane  0.17                                                                              8.76                                                                               1.61                                                                               0.32                                                                               3.67                                                                               0.01                                                                              2.55                                                                               2.15                                                                               0.10                                                                              10.47                                                                              2.69                                                                               2.10                                                                               2.33                Totals        98.2                                                                              95.8                                                                               96.9                                                                               97.8                                                                               94.9                                                                               97.9                                                                              97.8                                                                               97.5                                                                               98.9                                                                              97.9                                                                               98.1                                                                               98.3                                                                               98.2                % Conversion     99.9                                                                               99.9                                                                               93.0                                                                               99.0   100 100    99.0                                                                               100.0                                                                              100.0                                                                              100.0               % Selectivity    88.5                                                                               97.5                                                                               95.7                                                                               91.6   97.4                                                                               97.5   85.9                                                                               96.7                                                                               97.5                                                                               97.1                __________________________________________________________________________

EXAMPLES 24-29

In each of Examples 24-29, the liquid feed and a 5 weight percent palladium-on-carbon catalyst were charged to a flask and nitrogen was continuously passed through the reaction mixture to remove oxygen. The temperature of the reaction mixture was raised to the reaction temperature, and periodically samples were removed from the flask and analyzed. Hydrogen generated by the reaction was permitted to vent from the flask during the reaction. The experimental conditions employed, the compositions of the feedstock employed and of the resulting products containing up to 13 carbon atoms, the percent conversion of the feedstock, and the percent selectivity of the formation of desired product from the total amount of feedstock converted in each of Examples 24-29 are presented in Table 3.

The results in Table 3 illustrate that even with the mild temperature and pressure conditions employed in Examples 24-29, the dehydrogenation of the method of this invention affords both excellent conversion and selectivity.

                                      TABLE 3                                      __________________________________________________________________________                Feed                                                                               Example 24                                                                             Example 25                                                                             Feed                                                                               Ex. 26                                                                             Feed                                                                               Ex. 27                                                                             Feed                                                                               Ex. 28                                                                             Feed                                                                               Ex.                 __________________________________________________________________________                                                                29                  Conditions                                                                     Hours on stream                                                                               2.0 4.8 6.0 8.3     8.5     3.0     3.0     6.3                 Catalyst cycle no.                                                                            1   1   1   1       1       1       1       1                   Temperature (°C.)                                                                      242 243 245 244     251     253     254     254                 Pressure (psig)                                                                               1.0 1.0 1.0 1.0     0.0     0.0     0.0     1.0                 Feed/catalyst weight                                                                          10.0                                                                               10.0                                                                               50.0                                                                               50.0    100.0   49.9    100.0   10.0                ratio                                                                          Compositions (wt. %)                                                           1,4-DMT    0.0 0.0 0.0 0.0 0.0                 92.7                                                                               0.4                         1,5-DMT    92.0                                                                               2.2 0.0 4.2 1.9 93.9                                                                               1.1 0.5             1.2 0.0                 1,6-DMT    0.0 0.0 0.0 0.0 0.0 0.6     0.8             55.2                                                                               0.0                 1,7-DMT    0.0 0.0 0.0 0.0 0.0         89.4                                                                               0.4                                 1,8-DMT    0.0 0.0 0.0 0.0 0.0                         36.0                                                                               1.4                 other DMTs 0.1 0.4 0.2 0.3 0.0 1.2 0.3 0.1 0.0 0.0 3.6 1.0 0.0                 m-xylene   0.1 0.6 0.5 0.5 0.3 0.1 0.3 0.0 0.0             0.4                 non-cyclic 4.9 4.5 3.9 4.3 4.3 2.8 1.7 7.5 6.7 5.3 5.0 3.7 2.2                 Products                                                                       1,3-DMN    0.0 0.0 0.0 0.0 0.0     0.0 0.0 0.0 0.2 0.6     0.0                 1,4-DMN    0.0 0.0 0.0 0.0 0.0     0.0 0.0 0.2 1.6 90.2    0.0                 1,5-DMN    0.9 89.8                                                                               93.2                                                                               88.4                                                                               92.5                                                                               0.7 94.3                                                                               0.0 0.5             1.3                 1,6-DMN    0.0 0.5 0.5 0.4 0.0     0.8 0.0 0.8         0.9 58.2                1,7-DMN    0.0 0.0 0.0 0.0 0.0     0.1 1.5 90.5            0.6                 1,8-DMN    0.0 0.0 0.6 0.2 0.0     0.4 0.0 0.1             35.6                2,6- + 2,7-DMNs                                                                           0.0 0.0 0.0 0.0 0.0     0.0 0.0 0.3             0.2                 Lights     0.1 1.5 1.0 1.1 0.6     0.7 0.0 0.1 0.4         0.3                 Heavies    0.1 0.0 0.0 0.0 0.0     0.0 0.0 0.0         1.8 0.0                 Other      1.8 0.5 0.1 0.5 0.4 0.6 0.4 0.0 0.2     0.3     0.0                 Total      100.1                                                                              100.0                                                                              100.0                                                                              100.0                                                                              100.0                                                                              100.0                                                                              100.0                                                                              99.9                                                                               99.9                                                                               100.2                                                                              100.0                                                                              99.7                                                                               100.1               Total DMNs     90.3                                                                               94.3                                                                               89.0                                                                               92.5    95.5                                                                               1.5 92.4    90.8    95.8                % Conversion   97.6                                                                               100.0                                                                              95.4                                                                               98.0    98.8    99.5    99.5    98.5                % Selectivity  99  100 100 101     101     100     96.0    103.4               __________________________________________________________________________

EXAMPLES 30-47

In each of Examples 30-47, the particular isomer of dimethylnaphthalene employed as the feed was mixed in liquid form with unsupported catalyst in a stirred reaction vessel with a continuous nitrogen purge to preclude oxygen from the system. The temperature of the reaction vessel was raised to the reaction temperature and samples were withdrawn at various times after commencement of the reaction and analyzed. The conditions employed, the compositions of the feedstock employed and of the resulting products containing up to 13 carbon atoms, the percent conversion of the feedstock, and the percent selectivity of the formation of desired product from the total amount of feedstock converted in each of Examples 30-47 are presented in Table 4.

The catalyst employed in Example 30 was a crystalline borosilicate molecular sieve (HAMS-IB from Amoco Chemical). The catalyst employed in Example 31 was Union Carbide's LZ-Y20 ultra-stable Y-type sieve, containing 2 weight percent of copper, calculated as elemental copper. The catalyst employed in Example 32 was Union Carbide's LZ-Y62, a non-ultra-stable, Y-type sieve in the ammonia-exchanged form and having a unit cell size of 24.73Å. The catalyst employed in Examples 33 and 34 was commercially available Union Carbide's LZ-Y82, an ultra-stable molecular sieve having a unit cell size of 24.56Å and a sodium content of less than 0.2 weight percent. In Example 33, the sieve was in the ammonia form and had not been calcined. In Example 34, the sieve had been calcined to form the hydrogen form. The catalyst employed in Example 35 was a commercially available amorphous silica-alumina containing 13 weight percent of alumina. The catalyst employed in Example 36 was commercially available mordenite in the acid form. The catalyst employed in Examples 37, 38, 40-45 was commercially available Union Carbide's LZ-Y72 in the hydrogen form as received from the manufacturer. The catalyst employed in Example 39 was commercially available Grace USY sieve containing 2.6 weight percent of sodium and has chemical and physical properties that are very similar to those of Union Carbide's LZ-Y72, and is also suitable for use as a catalyst in either the cyclization or isomerization step in the method of this invention. 1,5-dimethylnaphthalene was the feed in Examples 30-44. The feed was 1,7-dimethylnaphthalene in Example 45 and 1,4-dimethylnaphthalene in Examples 46 and 47. For the purposes of Table 4, the concentration of 2,7-DMN in the product is taken to be approximately equal to the concentration of 1,7-DMN and is subtracted from the sum of 2,6-DMN and 2,7-DMN (which are determined together) for the purpose of determining the concentration of 2,6-DMN alone. The effective maximum concentrations of a particular desired DMN in its triad is its equilibrium concentration in the triad, which generally is 40-45 weight percent.

                                      TABLE 4                                      __________________________________________________________________________                     Feed                                                                               Ex. 30 Feed                                                                               Ex. 31                                                                              Feed                                                                               Ex. 32                                                                               Ex. 33                                                                               Ex.                                                                                  Ex.                  __________________________________________________________________________                                                               35                   Conditions                                                                     Temperature (°C.)                                                                           249        243      248   249   240   233                  Pressure (psig)     1          1        1     1     1     1                    Catalyst            Amsac-3400 LZ-20    LZ-Y62                                                                               LZ-Y82.sup.1                                                                         LZ-Y82.sup.2                                                                         SiO.sub.2 /                                         2% Cu                      Al.sub.2                                                                       O.sub.3              Feed/catalyst wt ratio                                                                             10         10       10.0  9.9   9.8   10.1                 Hours on stream     7.3        13       12    11.8  5.5   13                   Product Composition (wt. %)                                                    1,2-DMN         0.0 0.0    0.0 0.1  0.0 0.0   0.0   0.4   0.0                  1,3-DMN         0.0 0.0    0.0 0.0  0.0 0.0   0.0   0.0   0.0                  1,4-DMN         0.0 0.0    0.0 0.0  0.0 0.0   0.0   0.0   0.0                  1,5-DMN         93.4                                                                               69.3   82.6                                                                               8.7  82.6                                                                               82.3  75.6  4.1   21.9                 1,6-DMN         0.0 20.1   11.8                                                                               37.8 11.8                                                                               12.1  18.3  25.4  42.8                 1,7-DMN         0.0 0.0    1.2 1.5  1.2 1.3   1.2   3.6   1.2                  2,3-DMN         0.0 0.0    0.0 0.0  0.0 0.0   0.0   1.2   0.0                  2,6- + 2,7-DMNs 0.0 5.4    1.8 36.3 1.8 2.1   3.2   30.4  29.3                 Lights          6.3 2.6    1.7 1.4  1.7 1.8   1.2   1.3   1.2                  Heavies         0.0 1.9    0.2 5.8  0.2 0.1   0.1   16.2  1.2                  Naphthalene     0.0 0.0    0.0 0.1  0.0 0.0   0.0   0.7   0.0                  Methylnaphthalenes                                                                             0.0 0.2    0.6 6.5  0.6 0.3   0.2   12.7  2.0                  Other           0.2 0.5    0.0 1.9  0.0 0.0   0.0   3.9   0.5                  Total           99.9                                                                               100.0  99.9                                                                               100.1                                                                               99.6                                                                               100.1 99.8  100.1 100.1                Total DMNs      93.4                                                                               94.8   97.3                                                                               84.4 97.3                                                                               97.8  98.3  65.1  95.2                 2,7-DMN %                                                                      2,6-DMN % in the                                                                               0.0 5.7    0.6 42.8 0.6 0.9   2.1   47.7  30.3                 1,5-, 1,6- and 2,6-DMN triad                                                   2,6-DMN selectivity 100        71.7                 40.5  93.1                 __________________________________________________________________________                     Ex. 36                                                                               Ex. 37                                                                              Ex. 38                                                                              Ex. 39                                                                               Ex. 40                                                                              Ex. 41                                                                              Ex. 42                                                                              Ex.                                                                                 Ex.                  __________________________________________________________________________                                                               44                   Conditions                                                                     Temperature (°C.)                                                                       248   226  227  252   251  248  248  249  248                  Pressure (psig) 1     1    1    1     1    1    1    1    1                    Catalyst        Mordenite.sup.4                                                                      LZY-72                                                                              LZY-72                                                                              US-Y.sup.5                                                                           LZY-72                                                                               LZY-72                                                                             LZY-72                                                                              LZY-72                                                                              LZY-72               Feed/catalyst wt ratio                                                                         9.8   50.4 50.4 50.8  50.6 50.6 50.6 50.6 50.6                 Hours on stream 11.5  19.5 23.3 11.5  3.0  4.8  6.8  8.5  10.5                 Product Composition (wt. %)                                                    1,2-DMN         0.0   0.0  0.0  0.0   0.0  0.0  0.0  0.0  0.0                  1,3-DMN         0.0   0.0  0.0  0.0   0.0  0.0  0.0  0.0  0.0                  1,4-DMN         0.0   0.0  0.0  0.0   0.0  0.0  0.0  0.0  0.0                  1,5-DMN         41.2  24.0 21.3 17.5  20.9 15.1 12.2 9.6  8.7                  1,6-DMN         29.4  39.9 40.3 41.5  41.6 41.6 41.6 40.0 39.7                 1,7-DMN         0.7   1.0  0.9  1.0   0.9  1.0  1.0  1.2  1.2                  2,3-DMN         0.0   0.0  0.0  0.0   0.0  0.0  0.0  0.0  0.0                  2,6- + 2,7-DMNs 27.6  31.8 34.2 35.9  32.9 37.6 40.0 43.0 43.3                 Lights          1.0   1.9  0.9  1.2   1.6  1.6  1.2  1.0  1.1                  Heavies         0.0   0.9  1.1  1.0   0.8  1.1  1.6  2.1  2.2                  Naphthalene     0.0   0.0  0.0  0.0   0.0  0.0  0.0  0.0  0.0                  Methylnaphthalenes                                                                             0.1   1.0  1.1  1.3   1.1  1.5  1.7  2.6  2.8                  Other           0.0   0.4  0.2  0.5   0.3  0.5  0.7  0.5  0.9                  Total           100.0 100.9                                                                               100.0                                                                               99.9  100.1                                                                               100.0                                                                               100.0                                                                               100.0                                                                               99.9                 Total DMNs      98.9  96.7 96.7 95.9  96.3 95.2 94.8 93.9 93.0                 2,7-DMN %             1.1       1.1                       1.6                  2,6-DMN % in the                                                                               27.6  32.5 35.1 37.2  33.8 39.2 42.0 45.7 46.5                 1,5-, 1,6- and 2,6-DMN triad                                                   2,6-DMN selectivity                                                                            >100  99.5 99.9 97.3  98.4 95.6 94.6 92.3 90.5                 __________________________________________________________________________      Footnotes                                                                      .sup.1 not calcined                                                            .sup.2 calcined                                                                .sup.3 13% Al.sub.2 O.sub.3                                                    .sup.4 in H form                                                               .sup.5 ultra-stable sieve containing 2.6% Na                             

                                     Feed  Ex. 45                                                                               Feed  Ex. 46                                                                               Ex.                   __________________________________________________________________________                                                              47                                     Conditions                                                                     Temperature (°C.)                                                                             251         247   252                                    Pressure (psig)       1           1     1                                      Catalyst        LZY-72                                                                               LZY-72                                                                               LZY-72                                                                               LZY-72                                                                               LZY-72                                 Feed/catalyst wt ratio                                                                               50.0        44.0  44.0                                   Hours on stream       4.0         2.0   6.5                                    Product Composition (wt. %)                                                    1,2-DMN         0.0   0.0   0.0   0.1   0.4                                    1,3-DMN         0.0   0.0   0.6   50.8  51.0                                   1,4-DMN         0.0   0.0   90.6  15.1  9.0                                    1,5-DMN         0.5   0.2   0.0   0.0   0.0                                    1,6-DMN         0.7   1.4   0.0   0.0   0.0                                    1,7-DMN         90.4  40.5  0.0   0.0   0.1                                    2,3-DMN         0.0   0.0   0.0   22.1  23.3                                   2,6-DMN         0.0   1.3   0.0   0.0   0.3                                    2,7-DMN         0.3   44.7  0.0   0.0   0.1                                    Lights          6.6   6.3   5.2   4.3   3.6                                    Heavies         0.0   0.7   0.0   1.8   3.8                                    Naphthalene                 0.0   2.0   3.3                                    Methylnaphthalenes                                                                             0.2   1.7   3.6   3.9   4.8                                    Other           1.3   2.8   0.0   0.0   0.3                                    Total           100.0 99.6  100.0 100.1 100.0                                  Total DMNs      92.0  88.4  91.1  88.1  84.2                                   % desired DMN.sup.1 in its                                                                     0.3   52.2  0.6   25.1  28.0                                   triad                                                                          Selectivity           89.0        87.5  74.8                  __________________________________________________________________________      .sup.1 2,7-DMN in Example 45 and 2,3DMN in Examples 46-47.               

EXAMPLE 48

7.5 kilograms of distilled water, 7.5 kilograms of an aqueous solution containing 40 weight percent of tetraethylamine hydroxide, 50 grams of sodium hydroxide and 300 grams of sodium aluminate were stirred and dissolved in a 25-gallon stainless steel tank. The resulting solution and 12.2 kilograms of a silica sol containing 40 weight percent of silica were mixed and stirred in a 10-gallon autoclave at 150° C. for 72 hours. The resulting mixture was filtered, and the separated solids were washed three times with distilled water, dried at 120° C. and then calcined at 538° C. for 4 hours.

The resulting dried powder contained 0.37 weight percent of sodium, calculated as elemental sodium, and x-ray diffraction analysis indicated that the powder had the x-ray diffraction pattern of beta zeolite. The following is the x-ray diffraction pattern of the powder product, showing only the lines that are common to all 4 sources of beta zeolite in U.S. Pat. No. 3,308,069.

    ______________________________________                                                Line  Relative                                                                 d (A) Intensity                                                         ______________________________________                                                4.18  16.2                                                                     3.99  100.0                                                                    3.54  6.1                                                                      3.35  12.6                                                                     3.11  3.0                                                                      3.05  14.6                                                                     2.94  5.3                                                                      2.69  4.1                                                                      2.54  1.5                                                                      2.08  11.5                                                              ______________________________________                                    

The powder was employed as the catalyst without being ion-exchanged. Some powder was ion-exchanged using the procedure of Example 50 to reduce the sodium content, and after being ion-exchanged, the powder's alumina content, silica-to-alumina mole ratio and silicon-to-aluminum atom ratio were measured as 1.14 weight percent, 68:1 and 34:1, respectively.

EXAMPLE 49

8 kilograms of distilled water, 8 kilograms of an aqueous solution containing 40 weight percent of tetraethylamine hydroxide, 3.81 kilograms of an aqueous solution containing 20 weight percent of tetraethylamine hydroxide, 0.6 kilogram of sodium aluminate, and 12.2 kilograms of a silica sol containing 40 weight percent of silica were mixed and stirred in a 10-gallon autoclave at 150° C. for 72 hours. The resulting mixture was filtered, and the separated solids were washed three times with distilled water, dried at 120° C. for about 16 hours and then calcined at 538° C. for 6 hours.

The resulting dried powder contained 0.17 weight percent of sodium, calculated as elemental sodium. X-ray diffraction analysis indicated that the powder had the x-ray diffraction pattern of beta zeolite. The following is the x-ray diffraction pattern of the powder product, showing only the lines that are common to all 4 sources of beta zeolite in U.S. Pat. No. 3,308,069.

    ______________________________________                                                Line  Relative                                                                 d (A) Intensity                                                         ______________________________________                                                4.19  17.7                                                                     4.01  100.0                                                                    3.54  Weak                                                                     3.35  13.8                                                                     3.11  Weak                                                                     3.05  13.4                                                                     2.95   2.8                                                                     2.67  Weak                                                                     2.49   0.6                                                                     2.09   7.6                                                              ______________________________________                                    

The powder was employed as the catalyst without being ion-exchanged. After being ion-exchanged using the procedure of Example 50 in order to reduce the sodium content, the powder's silica-to-alumina mole ratio and silicon-to-aluminum atom ratio were measured as 30:1 and 14.8:1, respectively.

EXAMPLE 50

2.3 kilograms of the un-ion-exchanged catalyst powder produced in Example 49, 4 kilograms of distilled water, and 12 kilograms of an aqueous solution containing 19 weight percent of ammonium nitrate were stirred in a 22-liter flask at 72° C. for 4 hours. The mixture was then cooled; the liquid was removed by decantation, and the resulting ion-exchanged catalyst was then washed with water. The catalyst was then dried at 120° C. and calcined at 538° C. for 3 hours. The ion-exchanged catalyst contained 0.01 weight percent of sodium (calculated as elemental sodium), 2.43 weight percent of aluminum (calculated as elemental aluminum), and a silica-to-alumina mole ratio and a silicon-to-aluminum atomic ratio of 30:1 and 14.8:1, respectively.

163 grams of this dry, ion-exchanged beta zeolite powder, 454 grams of an alumina sol containing 8.8 weight percent of solids, and 123 grams of distilled water were blended to obtain a smooth, uniform slurry. The slurry was maintained at 23° C. for 5 hours to permit liquid to evaporate from the slurry. The slurry was then dried at 20° C. for about 16 hours and calcined at 538° C. for 2 hours, to afford solids containing 80 weight percent of beta zeolite and 20 weight percent of alumina, which were then ground and sieved to form particles having a 20-40 mesh size.

EXAMPLES 51-69

In each of Examples 51-69, the particular feedstock employed was mixed in liquid form with unsupported catalyst in a stirred reaction vessel with a continuous nitrogen purge to preclude oxygen from the system. The weight ratio of the feedstock-to-zeolite component of the catalyst was 49:1 in each case. The pressure of the contents of the reaction vessel was maintained at about 1 pound per square inch gauge. The temperature of the reaction vessel was raised to the reaction temperature and samples were withdrawn at various times after commencement of the reaction and analyzed. The conditions employed, the compositions of the feedstock employed and of the resulting products, the percent of the 1,5-, 1,6- and 2,6-DMN triad in each thereof, the percent of 2,6-DMN in each such 1,5-, 1,6- and 2,6-DMN triad, the percent decreases in each 1,5-, 1,6- and 2,6-DMN triad, the percent gains in each 1,7-, 1,8- and 2,7-DMN triad and the percent gain in total methylnaphthalene and trimethylnaphthalene content in each of Examples 51-69 are presented in Tables 5-9.

The catalyst employed in Examples 51-53 was commercially available Union Carbide's unsupported LZ-Y72 in the hydrogen form as received from the manufacturer. The catalyst employed in Examples 54-57 was an unsupported beta zeolite having a relatively high silicon-to-aluminum ratio and prepared by the procedure of Example 48. The catalyst employed in Examples 58-66 was an unsupported beta zeolite having a relatively low silicon-to-aluminum ratio and prepared by the procedure of Example 49. A single sample of this catalyst was used for four cycles in Examples 61-66. The catalyst employed in Examples 67-70 was also the beta zeolite having the relatively low silicon-to-aluminum ratio and prepared by the procedure of Example 49, but in this instance ion-exchanged to reduce the sodium content and supported on an alumina matrix by the procedure of Example 50.

                  TABLE 5                                                          ______________________________________                                                     Feed  Ex. 51   Ex. 52   Ex. 53                                     ______________________________________                                         Conditions                                                                     Catalyst              LZ-Y72   LZ-Y72 LZ-Y72                                   Temperature (°C.)                                                                             250      250    250                                      Hours on Stream       1        3      4.75                                     Product Composition                                                            (wt. %)                                                                        1,5-DMN       91.03   38.70    18.30  12.84                                    1,6-DMN       3.73    36.92    40.67  40.35                                    2,6-DMN       0       18.42    32.40  36.18                                    1,7-DMN       0.74    0.81     0.93   1.08                                     2,7-DMN       0       0.73     1.37   1.81                                     Methylnaphthalenes                                                                           0.06    0.62     1.43   2.03                                     Trimethylnaphthalenes                                                                        0.44    0.53     1.33   2.02                                     Other         4.00    3.27     3.57   3.69                                     Total         100.00  100.00   100.00 100.00                                   1,5-, 1,6- and                                                                               94.76   94.04    91.37  89.37                                    2,6-DMN triad content                                                          2,6-DMN percent in                                                                           0       19.59    35.46  40.49                                    1,5-, 1,6- and 2,6-DMN                                                         triad                                                                          1,5-, 1,6- and 2,6-DMN                                                                       0       0.72     3.39   5.39                                     triad percent loss                                                             1,7-, 1,8- and 2,7-DMN                                                                       0       0.80     1.56   2.15                                     triad percent gain                                                             Methylnaphthalene and                                                                        0       0.71     2.32   3.61                                     trimethylnaphthalene                                                           percent gain                                                                   ______________________________________                                    

                  TABLE 6                                                          ______________________________________                                                    Feed  Ex. 54  Ex. 55  Ex. 56                                                                               Ex. 57                                  ______________________________________                                         Conditions                                                                     Catalyst from        48      48    48    48                                    Example                                                                        Temperature (°C.)                                                                            250     250   250   250                                   Hours on Stream      1       3     5     7                                     Product Composition                                                            (wt. %)                                                                        1,5-DMN      91.03   54.00   28.93 18.94 14.09                                 1,6-DMN      3.73    28.76   37.62 39.70 40.41                                 2,6-DMN      0       0       12.91 28.63 35.96                                 1,7-DMN      0.74    0.61    0.58  0.60  0.67                                  2,7-DMN      0       0.67    1.09  1.13  1.28                                  Methylnaphthalenes                                                                          0       0.12    0.29  0.41  0.57                                  Trimethylnaphthalenes                                                                       0.44    0.10    0.19  0.34  0.46                                  Other        4.06    2.83    2.67  2.92  2.97                                  Total        100.00  100.00  100.00                                                                               100.00                                                                               100.00                                1,5-, 1,6- and                                                                              94.76   95.67   95.18 94.60 94.05                                 2,6-DMN triad                                                                  content                                                                        2,6-DMN percent in                                                                          0       13.49   30.08 38.01 42.05                                 1,5-, 1,6- and                                                                 2,6-DMN triad                                                                  1,5-, 1,6- and                                                                              0       -0.91   -0.42 0.16  0.71                                  2,6-DMN triad                                                                  percent loss                                                                   1,7-, 1,8- and                                                                              0       0.54    0.93  0.99  1.21                                  2,7-DMN triad                                                                  percent gain                                                                   Methylnaphthalene                                                                           0       -0.23   0.04  0.31  0.59                                  and trimethyl-                                                                 naphthalene percent                                                            gain                                                                           ______________________________________                                    

                  TABLE 7                                                          ______________________________________                                                        Feed  Ex. 58  Ex. 59  Ex. 60                                    ______________________________________                                         Conditions                                                                     Catalyst from Example    49      49    49                                      Temperature (°C.) 250     250   250                                     Hours on Stream          1.25    3     5                                       Product Composition (wt. %)                                                    1,5-DMN          91.03   21.94   10.79 8.20                                    1,6-DMN          3.73    38.62   40.89 41.20                                   2,6-DMN          0       35.59   43.28 44.94                                   1,7-DMN          0.74    0.52    0.60  0.64                                    2,7-DMN          0       0.30    0.53  0.47                                    Methylnaphthalenes                                                                              0       0.33    0.59  0.84                                    Trimethylnaphthalenes                                                                           0.44    0.16    0.46  0.78                                    Other            4.06    2.54    2.86  2.93                                    Total            100.00  100.00  100.00                                                                               100.00                                  1,5-, 1,6- and   94.76   96.15   94.96 94.34                                   2,6-DMN triad content                                                          2,6-DMN percent in 1,5-, 1,6-                                                                   0       37.02   45.58 47.63                                   and 2,6-DMN triad                                                              1,5-, 1,6- and 2,6-DMN                                                                          0       -1.39   -0.20 0.42                                    triad percent loss                                                             1,7-, 1,8- and 2,7-DMN                                                                          0       0.08    0.39  0.37                                    triad percent gain                                                             Methylnaphthalene and                                                                           0       0.05    0.61  1.18                                    trimethylnaphthalene                                                           percent gain                                                                   ______________________________________                                    

                                      TABLE 8                                      __________________________________________________________________________                    Feed                                                                               Ex. 61                                                                             Ex. 62                                                                             Ex. 63                                                                             Feed                                                                               Ex. 64                                                                             Ex. 65                                                                             Ex. 66                              __________________________________________________________________________     Conditions                                                                     Catalyst from Example                                                                             49  49  49      49  49  49                                  Temperature (°C.)                                                                          240 240 240     240 265 265                                 Hours on Stream    3   3.9 3       45  3   4.5                                 Catalyst Cycle     1st 1st 3rd     3rd 4th 4th                                 Product Composition (wt. %)                                                    1,5-DMN        88.14                                                                              9.63                                                                               7.99                                                                               26.62                                                                              88.14                                                                              17.73                                                                              11.47                                                                              8.16                                1,6-DMN        3.66                                                                               39.45                                                                              39.53                                                                              35.39                                                                              3.66                                                                               38.10                                                                              39.23                                                                              39.73                               2,6-DMN        0   41.50                                                                              42.34                                                                              29.83                                                                              0   36.25                                                                              40.02                                                                              42.31                               1,7-DMN        0.74                                                                               0.66                                                                               0.69                                                                               0.57                                                                               0.74                                                                               0.59                                                                               0.66                                                                               0.72                                2,7-DMN        0   1.26                                                                               1.50                                                                               1.02                                                                               0   0.97                                                                               1.20                                                                               1.13                                Methylnaphthalenes                                                                            0.13                                                                               0.99                                                                               1.17                                                                               0.26                                                                               0.13                                                                               0.33                                                                               0.48                                                                               0.70                                Trimethylnaphthalenes                                                                         0.54                                                                               0.53                                                                               0.70                                                                               0.17                                                                               0.54                                                                               0.29                                                                               0.37                                                                               0.52                                Other          6.79                                                                               5.98                                                                               6.08                                                                               6.14                                                                               6.79                                                                               5.74                                                                               6.57                                                                               6.73                                Total          100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                              1,5-, 1,6- and 91.80                                                                              90.58                                                                              89.86                                                                              91.84                                                                              91.80                                                                              92.08                                                                              90.72                                                                              90.20                               2,6-DMN triad content                                                          2,6-DMN percent in 1,5-, 1,6-                                                                 0   45.82                                                                              47.12                                                                              32.48                                                                              0   39.37                                                                              44.11                                                                              46.91                               and 2,6-DMN triad                                                              1,5-, 1,6- and 2,6-DMN                                                                        0   1.22                                                                               1.94                                                                               -0.04                                                                              0   -0.28                                                                              1.08                                                                               1.60                                triad percent loss                                                             1,7-, 1,8- and 2,7-DMN                                                                        0   1.18                                                                               1.45                                                                               0.85                                                                               0   0.82                                                                               1.12                                                                               1.11                                triad percent gain                                                             Methylnaphthalene and                                                                         0   0.85                                                                               1.20                                                                               -0.24                                                                              0   -0.05                                                                              0.18                                                                               0.55                                trimethylnaphthalene                                                           percent gain                                                                   __________________________________________________________________________

                  TABLE 9                                                          ______________________________________                                                        Feed  Ex. 67  Ex. 68  Ex. 69                                    ______________________________________                                         Conditions                                                                     Catalyst from Example    50      50    50                                      Temperature (°C.) 250     250   250                                     Hours on Stream          1       2     3                                       Product Composition (wt. %)                                                    1,5-DMN          88.14   16.50   11.20 9.23                                    1,6-DMN          3.66    38.10   39.30 39.70                                   2,6-DMN          0       37.42   41.07 42.15                                   1,7-DMN          0.74    0.53    0.55  0.58                                    2,7-DMN          0       0.97    0.84  1.00                                    Methylnaphthalenes                                                                              0.13    0.52    0.69  0.83                                    Trimethylnaphthalenes                                                                           0.54    0.32    0.62  0.75                                    Other            6.79    5.64    5.73  5.76                                    Total            100.00  100.00  100.00                                                                               100.00                                  1,5-, 1,6- and   91.80   92.02   91.57 91.08                                   2,6-DMN triad content                                                          2,6-DMN percent in 1,5-, 1,6-                                                                   0       40.67   44.85 46.28                                   and 2,6-DMN triad                                                              1,5-, 1,6- and 2,6-DMN                                                                          0       -0.22   0.23  0.72                                    triad percent loss                                                             1,7-, 1,8- and 2,7-DMN                                                                          0       0.76    0.65  0.84                                    triad percent gain                                                             Methylnaphthalene and                                                                           0       0.17    0.64  0.91                                    trimethylnaphthalene                                                           percent gain                                                                   ______________________________________                                    

Comparison of the results in Tables 5-9 illustrates clearly that (1) the use of a beta zeolite catalyst affords reduced losses of the 1,5-, 1,6- and 2,6-dimethylnaphthalene triad, reduced formation of methylnaphthalenes, trimethylnaphthalenes and the 1,7-, 1,8- and 2,7-dimethylnaphthalene triad relative to the use of the LZ-Y72 zeolite catalyst; and (2) the use of a beta zeolite catalyst either unsupported or supported on a base material and having a relatively lower silicon-to-aluminum ratio affords greater formation of 2,6-dimethylnaphthalene and reduced losses of the 1,5-, 1,6- and 2,6-dimethylnaphthalene triad relative to the use of a beta zeolite catalyst having a relatively higher silicon-to-aluminum ratio and permits the use of lower reaction temperatures or the use at a higher temperature of even a partially deactivated catalyst relative to the use of a LZ-Y72 zeolite catalyst.

EXAMPLES 70-77

In each of Examples 70-77 a fixed bed reactor was used to evaluate a continuous process for the dehydrogenation of a feedstock containing 1,5-dimethyltetralin (1,5-DMT) to yield mainly 1,5-dimethylnaphthalene (1,5-DMN). The fixed bed reactor used was a 13 centimeter long stainless steel tube having a 0.20 centimeter inside diameter and packed with 3.15 grams of a catalyst containing 0.35 wt % platinum and 0.35 wt % rhenium on a 16-25 mesh gamma alumina support. Preheated feedstocks having the compositions shown in Tables 10 and 11 were pumped upflow through the catalyst bed in the reactor tube at the reaction conditions listed in Tables 10 and 11, respectively. Thermocouples installed in the reactor inlet and exit monitored the reaction temperature. Heating tape wrapped around the reactor tube was used to maintain the set reaction temperature. Reaction pressure was maintained to keep the feedstock and hydrocarbon products as liquids. Reactor effluent was collected in a 300 ml pressure vessel maintained at 70°-100° C. to keep the product mixture liquid. The hydrogen gas generated by the dehydrogenation reaction was vented continuously from the collection vessel through a pressure regulator.

The selectivity and conversion percentages presented in Tables 10 and 11 were calculated according to the following equations: (1,6-DMN is in the 1,5-, 1,6-, 2,6-DMN triad and can be isomerized to 2,6-DMN; consequently, 1,6-DMT and 1,6-DMN wt. percentages are included in the following equations.) ##EQU1##

Table 10 reports data for the single-pass conversion of the 1,5-DMT containing feedstock to 1,5-DMN containing product. Table 11 reports data for the single-pass conversion of a 1,5-DMT containing feedstock that was distilled to remove heavy components before subjecting the feedstock to the dehydrogenation reaction. Table 11 also reports data for a two-pass conversion of the 1,5-DMT containing feedstock. In the two-pass conversion procedure the product stream from the single-pass dehydrogenation reaction was collected and passed through the fixed bed dehydrogenation reactor a second time. This two-pass procedure simulates a process utilizing two or more fixed bed dehydrogenation reactors in series wherein the hydrogen formed by the dehydrogenation reaction is partially or totally vented between reactors.

                                      TABLE 10                                     __________________________________________________________________________                   Feed                                                                               Ex. 70                                                                             Ex. 71                                                                             Ex. 72                                                                             Ex. 73                                                                             Ex. 74                                                                             Ex. 75                                   __________________________________________________________________________     Conditions                                                                     Hours on stream   436 441 482 503 957 1223                                     Catalyst cycle no.                                                                               2   2   2   2   2   2                                        Temperature (°C.)                                                                         401 400 400 401 400 400                                      Pressure (psig)   201 201 202 201 170 178                                      WHSV (grams feed/hr/gram                                                                         4.14                                                                               2.07                                                                               0.54                                                                               1.07                                                                               2.12                                                                               2.13                                     catalyst)                                                                      Composition (wt %)                                                             1,5-DMT       84.66                                                                              4.56                                                                               3.90                                                                               1.90                                                                               3.51                                                                               3.17                                                                               7.59                                     1,6-DMT       0.91                                                                               0.07                                                                               0.12                                                                               0.21                                                                               0.15                                                                               0.06                                                                               0.09                                     2,6- + 2,7- + 1,7-DMT                                                                        0.27                                                                               0.00                                                                               0.00                                                                               0.06                                                                               0.00                                                                               0.00                                                                               0.00                                     2,8-DMT       0.68                                                                               0.31                                                                               0.16                                                                               0.00                                                                               0.16                                                                               0.20                                                                               0.00                                     2,5- + 1,8-DMT                                                                               0.31                                                                               0.00                                                                               0.11                                                                               0.22                                                                               0.00                                                                               0.08                                                                               0.23                                     Lights        0.24                                                                               1.68                                                                               2.36                                                                               9.61                                                                               3.31                                                                               2.05                                                                               1.54                                     C.sub.12 Indane                                                                              1.06                                                                               1.70                                                                               2.10                                                                               2.08                                                                               2.56                                                                               1.82                                                                               1.78                                     o-Tolylpentane                                                                               3.20                                                                               3.68                                                                               3.78                                                                               2.48                                                                               3.74                                                                               3.78                                                                               3.77                                     Products                                                                       1,5-DMN       1.64                                                                               80.15                                                                              77.48                                                                              51.95                                                                              71.46                                                                              78.97                                                                              75.68                                    1,6-DMN       0.07                                                                               2.37                                                                               4.18                                                                               11.20                                                                              6.54                                                                               3.72                                                                               3.09                                     1,7-DMN       0.00                                                                               0.42                                                                               0.62                                                                               1.29                                                                               0.78                                                                               0.59                                                                               0.50                                     1,8-DMN       0.00                                                                               0.18                                                                               0.11                                                                               0.04                                                                               0.04                                                                               0.05                                                                               0.18                                     2,6- + 2,7-DMN                                                                               0.00                                                                               0.00                                                                               0.10                                                                               0.79                                                                               0.23                                                                               0.09                                                                               0.16                                     1-Methylnaphthalene                                                                          0.00                                                                               0.57                                                                               1.15                                                                               7.60                                                                               2.09                                                                               0.79                                                                               0.65                                     2-Methylnaphthalene                                                                          0.00                                                                               0.00                                                                               0.00                                                                               0.29                                                                               0.10                                                                               0.06                                                                               0.05                                     Heavies       6.69                                                                               3.38                                                                               2.23                                                                               2.08                                                                               2.48                                                                               2.23                                                                               2.18                                     Others        0.27                                                                               0.94                                                                               1.62                                                                               8.22                                                                               2.85                                                                               2.33                                                                               2.52                                     Total         100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                   % Conversion  --  94.6                                                                               95.3                                                                               97.5                                                                               95.7                                                                               96.2                                                                               91.0                                     % Selectivity --  99.8                                                                               98.0                                                                               73.6                                                                               93.1                                                                               98.3                                                                               98.9                                     __________________________________________________________________________

                  TABLE 11                                                         ______________________________________                                                          Ex. 76   Ex. 77    Over-                                                 Feed  (1st pass)                                                                              (2nd pass)                                                                               all                                        ______________________________________                                         Conditions                                                                     Hours on stream       477      740                                             Catalyst cycle no.    3        3                                               Temperature (°C.)                                                                             400      401                                             Pressure (psig)       200      200                                             WHSV (grams feed/hr/  4.30     4.36                                            gram catalyst)                                                                 Composition (wt %)                                                             1,5-DMT       83.16   7.78     1.05                                            1,6-DMT       2.79    0.20     0.04                                            2,6- + 2,7- + 1,7-DMT                                                                        0.87    0.06     0.00                                            2,8-DMT       0.82    0.45     0.06                                            2,5- + 1,8-DMT                                                                               0.87    0.20     0.05                                            Lights        0.46    1.34     1.49                                            C.sub.12 Indane                                                                              1.52    1.71     1.65                                            o-Tolylpentane                                                                               4.88    5.04     4.67                                            Products                                                                       1,5-DMN       2.02    76.00    79.30                                           1,6-DMN       0.36    4.51     7.17                                            1,7-DMN       0.03    0.88     1.24                                            1,8-DMN       0.01    0.17     0.12                                            2,6- + 2,7--DMN                                                                              0.08    0.18     0.33                                            1-Methylnaphthalene                                                                          0.00    0.28     1.19                                            2-Methylnaphthalene                                                                          0.06    0.01     0.05                                            Heavies       0.17    0.45     0.80                                            Others        1.70    0.75     0.78                                            Total         100.00  100.00   100.00                                          % Conversion  --      90.7     86.4    98.7                                    % Selectivity --      100.0    86.5    98.9                                    ______________________________________                                    

Examples 70-73 demonstrate that high conversions are possible at a wide range of flow rates (WHSV) of from about 0.54 to about 4.14 grams of feed per gram of catalyst per hour using a continuous dehydrogenation procedure. As the flow rates increase the conversion decreases; however, the selectivity to 1,5- and 1,6-DMN increases. Example 74 and 75 demonstrate that even after many hours of liquid phase operation high conversion and selectivities are maintained at a reaction temperature of about 400° C. Noble metal catalysts in general require the addition of large amounts of hydrogen to maintain catalytic activity for prolonged periods. However, by employing reaction conditions in the dehydrogenation method of this invention such that a liquid reaction mixture was maintained, additional hydrogen was not required to maintain catalyst activity In commercial operation, expensive hydrogen recycle equipment would not, therefore, be required. Examples 76 and 77 demonstrate that the continuous dehydrogenation reaction can be run in at least a two-pass process wherein the product stream from the first pass through the reactor, after the removal of hydrogen, is feed to a second fixed bed reactor. This type of operation can promote the dehydrogenation reaction by providing for the removal of hydrogen between reactors and thereby increasing the conversion and selectivity of the dehydrogenation reaction of this invention. By using this two-pass process conversion was increased from 90.7% for the first pass to 98.7% after the second pass, as demonstrated by a comparison of the data from Example 76 in Table 11 to the overall conversion reported in Table 11.

From the above description, it is apparent that the objects of the present invention have been achieved While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These alternatives are considered equivalents and are within the spirit and scope of the present invention. 

Having described the invention, what is claimed is:
 1. A method for preparing one or more dimethyltetralins from 5-(o-,m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene as the first feedstock, comprising: contacting the first feedstock in liquid form with a solid cyclization catalyst comprising an acidic ultra-stable crystalline aluminosilicate molecular sieve Y-zeolite that has a silica-to-alumina molar ratio of from about 4:1 to about 10:1, pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from 24.2 to about 24.7 angstroms, and that contains from about 0.05 up to about 3.5 weight percent of sodium, calculated as elemental sodium, and based on the weight of the zeolite and that is substantially free of adsorbed water, and at an elevated temperature and at a pressure that is sufficiently high to maintain the first feedstock substantially in the liquid phase, to thereby cyclize the first feedstock to form a first liquid product comprising one or more dimethyltetralins, wherein water is at a concentration in the first feedstock of from zero up to less than about 0.5 weight percent, based on the weight of the feedstock, wherein (1) when the first feedstock comprises 5-(o-tolyl)-pent-1 or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,5-, 1,6-, 2,5- or 2,6-dimethyltetralin or a mixture thereof, (2) when the first feedstock comprises 5-(m-tolyl)-pent-1 or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,5-, 1,6-, 1,7-, 1,8-, 2,5-, 2,6-, 2,7- or 2,8-dimethyltetralin or a mixture thereof, (3) when the first feedstock comprises 5-(p-tolyl)-pent-1 or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised by 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof, or (4) when the first feedstock comprises 5-phenyl-hex-1- or -2-ene, at least 80 weight percent of the dimethyltetralin product formed is comprised of 1,3-, 1,4-, 2,3-, 5,7-, 5,8- or 6,7-dimethyltetralin or a mixture thereof.
 2. The method of claim 1 wherein the first feedstock comprises 5-(o-tolyl)-pent-1- or -2-ene and at least 80 weight percent of the dimethyltetralin product formed comprises 1,5-, 1,6-, 2,5- or 2,6-dimethyltetralin or a mixture thereof.
 3. The method of claim 1 wherein the first feedstock comprises 5-(m-tolyl)-pent-1- or -2-ene and at least 80 weight percent of the dimethyltetralin product formed comprises 1,5-, 1,6-, 1,7-, 1,8- 2,5-, 2,6-, 2,7-, or 2,8-dimethyltetralin or a mixture thereof.
 4. The method of claim 1 wherein the first feedstock comprises 5-(p-tolyl)-pent-1- or -2-ene and at least 80 weight percent of the dimethyltetralin product formed comprises 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof.
 5. The method of claim 1 wherein the first feedstock comprises 5-phenyl-hex-1- or -2-ene and at least 80 weight percent of the dimethyltetralin product formed comprises 1,3-, 1,4-, 2,3-, 5,7-, 5,8-, or 6,7-dimethyltetralin or a mixture thereof.
 6. The method of claim 1 wherein the cyclization is performed at a temperature in the range of from about 120° C. to about 400° C.
 7. The method of claim 1 wherein the cyclization is performed on a batch basis.
 8. The method of claim 1 wherein the cyclization step is performed batchwise, and the cyclization catalyst comprises from about 1 to about 3.5 weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite.
 9. The method of claim 1 wherein the cyclization step is performed continuously, and the cyclization catalyst comprises from about 0.05 to about 0.5 weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite.
 10. The method of claim 1 wherein the molecular sieve Y-zeolite is in the hydrogen form and contains additionally from about 0.05 to about 3 weight percent of a noble metal component selected from the group consisting of platinum, palladium, iridium, and rhodium, calculated as the elemental metal, and on the basis of the weight of the cyclization catalyst.
 11. The method of claim 10 wherein the noble metal component of the molecular Y-sieve zeolite comprises platinum.
 12. The method of claim 10 wherein the cyclization catalyst also comprises from about 0.01 to about 5 weight percent of a component comprising a transition metal selected from the group consisting of copper, tin, gold, lead and silver, calculated as the elemental metal and based on the weight of the catalyst.
 13. The method of claim 12 wherein the transition metal component of the molecular sieve Y-zeolite comprises copper.
 14. The method of claim 1 wherein the cyclization catalyst is free of a support material.
 15. The method of claim 1 wherein the cyclization catalyst is supported on an inert, porous refractory, inorganic oxide support material.
 16. The method of claim 15 wherein the support material comprises silica, alumina, bentonite, magnesia, or silica-alumina, or a mixture thereof.
 17. The method of claim 1 wherein the cyclization is performed on a continuous basis with a space velocity of, or on a batch basis with an effective space velocity of, from about 0.01 to about 20 parts of feedstock per part of the zeolite component of the cyclization catalyst by weight per hour.
 18. The method of claim 1 wherein the cyclization is performed on a batch basis, the cyclization catalyst is employed at a level in the range of from 0.1 to about 5.0 weight percent of the zeolite component of the catalyst based on the weight of the feedstock, and the reaction time is from about 0.5 to about 10 hours.
 19. The method of claim 1 wherein the cyclization catalyst employed in the cyclization contains less than 15 weight percent of water adsorbed thereon based on the weight of the zeolite component thereof.
 20. The method of claim 1 wherein the first feedstock is dissolved in a solvent.
 21. The method of claim 20 wherein the solvent is a paraffin or aromatic hydrocarbon which boils above 270° C.
 22. A method for preparing one or more of dimethylnaphthalenes comprising contacting the first liquid product from claim 1 as a second feedstock in liquid form with a solid dehydrogenation catalyst in a reaction vessel at an elevated temperature and at a pressure that is sufficiently high to maintain the second feedstock substantially in the liquid phase, to thereby affect conversion of the aforesaid first liquid product in an equilibrium dehydrogenation reaction to form hydrogen and a second liquid product comprising said one or more dimethylnaphthalenes, and removing a substantial portion of the hydrogen being formed in the dehydrogenation reaction from the reaction vessel to thereby shift the aforesaid equilibrium toward the formation of the aforesaid one or more dimethylnaphthalenes, wherein (a) when 1,5-, 1,6-, 2,5-, or 2,6-dimethyltetralin or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product formed in (1) of claim 1 and present in the second feedstock, at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,5-, 1,6- or 2,6-dimethylnaphthalene or a mixture thereof, or (b) when 1,5-, 1,6-, 1,7-, 1,8- 2,5-, 2,6-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product formed in (2) of claim 1 and present in the second feedstock, at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,5-, 1,6-, 1,7-, 1,8-, 2,6- or 2,7-dimethylnaphthalene or a mixture thereof or (c) when 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product formed in (3) of claim 1 and present in the second feedstock, at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,7-, 1,8-, or 2,7-dimethylnaphthalene or a mixture thereof or (d) when 1,3-, 1,4-, 2,3-, 5,7-, 5,8- or 6,7-dimethyltetralin or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product formed in (4) of claim 1 and present in the second feedstock, at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,3-, 1,4- or 2,3-dimethylnaphthalene or a mixture thereof.
 23. The method of claim 22 wherein 1,5-, 1,6-, 2,5-, or 2,6-dimethyltetralin, or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product present in the second feedstock and at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,5-, 1,6-, or 2,6-dimethylnaphthalene or a mixture thereof.
 24. The method of claim 22 wherein 1,5-, 1,6-, 1,7-, 1,8-, 2,5-, 2,6-, 2,7-, or 2,8-dimethyltetralin, or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product present in the second feedstock and at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,5-, 1,6-, 1,7-, 1,8-, 2,6- or 2,7-dimethylnaphthalene or a mix thereof.
 25. The method of claim 22 wherein 1,7-, 1,8-, 2,7-, or 2,8-dimethyltetralin, or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product present in the second feedstock and at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,7-, 1,8-, or 2,7-dimethylnaphthalene or a mixture thereof.
 26. The method of claim 22 wherein 1,3-, 1,4-, 2,3-, 5,7-, 5,8- or 6,7-dimethyltetralin, or a mixture thereof comprises at least 80 weight percent of the dimethyltetralin product present in the second feedstock and at least 80 weight percent of the dimethylnaphthalene product in the second liquid product is comprised of 1,3-, 1,4-, or 2,3-dimethylnaphthalene or a mixture thereof.
 27. The method of claim 22 wherein the dehydrogenation is performed at a temperature in the range of from about 200° C. to about 500° C.
 28. The method of claim 22 wherein the dehydrogenation is performed at a pressure in the range of from about 0.1 to about 30 atmospheres absolute.
 29. The method of claim 22 wherein the dehydrogenation catalyst comprises a noble metal component supported on a substantially inert support material, with the noble metal component employed at a level of from about 0.5 to about 15 weight percent, calculated as the elemental noble metal and based on the weight of the dehydrogenation catalyst.
 30. The method of claim 29 wherein the noble metal component comprises palladium.
 31. The method of claim 29 wherein the dehydrogenation is performed continuously with a space velocity in the range of from about 0.1 to about 5000 parts of the feedstock per part of the noble metal component of the dehydrogenation catalyst by weight per hour.
 32. The method of claim 29 wherein the dehydrogenation is performed on a batch basis with the dehydrogenation catalyst at a level in the range of from about 0.005 to about 1.0 percent of the noble metal component, calculated as the elemental noble metal, and based on the weight of the dimethyltetralin feedstock and the reaction time is from about 1 to about 50 hours.
 33. The method of claim 22 wherein the second feedstock is dissolved in a solvent.
 34. The method of claim 33 wherein the solvent is a paraffin or aromatic hydrocarbon which boils above about 270° C.
 35. A method for isomerizing at least 20 weight percent of the total of (1) the 1,5-, and 1,6-dimethylnaphthalenes in the second liquid product in (a) of claim 22 to 2,6-dimethylnaphthalene, (2) the 1,5-, 1,6-, 1,7-, and 1,8-dimethylnaphthalenes in the aforesaid second liquid product in (b) of claim 22 to 2,7-dimethylnaphthalene and 2,6-dimethylnaphthalene, (3) the 1,7- and 1,8-dimethylnaphthalene in the aforesaid second liquid product in (c) of claim 22 to 2,7-dimethylnaphthalene, or (4) the 1,3- and 1,4-dimethylnaphthalene in the aforesaid second liquid product in (d) of claim 22 to 2,3-dimethylnaphthalene, comprising: contacting the aforesaid second liquid product in liquid form with a solid isomerization catalyst comprising either beta zeolite or an acidic ultrastable crystalline Y-zeolite having a silica-to-alumina molar ratio of from about 4:1 to about 10:1, having pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from about 24.2 to about 24.7 angstroms, and at an elevated temperature and at a pressure that is sufficiently high to maintain the isomerization feedstock substantially in the liquid phase.
 36. The method of claim 35 wherein at least 25 weight percent of the total of 1,5- and 1,6-dimethylnaphthalenes in the aforesaid second liquid product in (a) of claim 22 is isomerized to 2,6-dimethylnaphthalene.
 37. The method of claim 35 wherein at least 25 weight percent of the total of 1,5-, 1,6-, 1,7- and 1,8-dimethylnaphthalenes in the aforesaid second liquid product in (b) of claim 22 is isomerized to 2,7-dimethylnaphthalene and 2,6-dimethylnaphthalene.
 38. The method of claim 35 wherein at least 25 weight percent of the total of 1,7- and-1,8-dimethylnaphthalenes in the aforesaid second liquid product in (c) of claim 22 is isomerized to 2,7-dimethylnaphthalene.
 39. The method of claim 35 wherein at least 25 weight percent of the total of 1,3- and 1,4-dimethylnaphthalenes in the aforesaid second liquid product feedstock in (d) of claim 22 is isomerized to 2,3-dimethylnaphthalene.
 40. The method of claim 35 wherein the isomerization is performed at a temperature in the range of from about 200° C. to about 420° C.
 41. The method of claim 35 wherein the isomerization is performed on a batch basis.
 42. The method of claim 35 wherein the isomerization catalyst employed comprises beta zeolite.
 43. The method of claim 42 wherein the isomerization catalyst comprises a hydrogenation component comprising a Group VIII metal.
 44. The method of claim 43 wherein the Group VIII metal is palladium, platinum or nickel.
 45. The method of claim 35 wherein the isomerization catalyst employed is free of a support material.
 46. The method of claim 35 wherein the isomerization catalyst is supported on an inorganic support material.
 47. The method of claim 46 wherein the support material comprises silica, alumina, silica-alumina, or bentonite, or magnesia, or a mixture thereof.
 48. The method of claim 35 wherein the isomerization is performed at a pressure in the range of from about 0.1 to about 20 atmospheres absolute.
 49. The method of claim 35 wherein the isomerization is performed on a continuous basis with a space velocity of, or on a batch basis with an effective space velocity of, from about 0.1 to about 20 parts of feedstock per part of the zeolite component of the isomerization catalyst by weight per hour.
 50. The method of claim 22 wherein the dehydrogenation catalyst comprises a mixture of platinum and rhenium supported on an alumina support.
 51. The method of claim 50 wherein the platinum and rhenium are each present in an amount of about 0.01 to about 10.0 weight percent calculated based on the weight of the catalyst and wherein the alumina support comprises gamma alumina.
 52. The method of claim 22 wherein the dehydrogenation reaction is performed continuously using at least two series arranged fixed bed reactors and wherein hydrogen is removed from the liquid product between the fixed bed reactors. 